The present invention generally relates to drive trains, such as those used in Electrophotographic Printing (EP) systems, and particularly relates to characterizing and compensating them for improved speed control.
Drive trains may be broadly understood as comprising a drive element or assembly that provides motive force at a drive output. A typical drive train provides one or more control inputs that allow control of its speed and/or direction, and an extraordinarily broad range of devices or systems use such drive trains for a variety of purposes.
In EP systems, for example, the typical drive train comprises some type of drive assembly configured to drive one or more rotating members, such as developer rollers, Image Transfer Medium (ITM) belts, Photoconductive (PC) drums or PC belts, or paper transport belts. In particular, EP systems typically use replaceable cartridges providing consumables used in the EP process, such as toner cartridges that include toner stores, developer rollers and PC drums driven by one or more drive trains integrated within the cartridge.
An EP system adapted to use such cartridges typically includes corresponding mechanical and electrical cartridge interfaces, such as a motor drive interface configured to provide mechanical and/or electrical inputs to the cartridge. In this context, the typical EP system generates motor control signals operative to run the cartridge drive train motor at desired velocities, and which may effect desired velocity profiles for target EP process speeds. It is common, for example, to implement speed controls that run the drive train motor at a target speed corresponding to a desired EP process speed. Since different printing resolutions typically require different process speeds, a multi-resolution EP system may have multiple process speed targets.
Regardless, the ability to maintain a given target speed represents an important determinant of printing quality. In particular, variations in the velocity of printing process members, such as a PC drum, during the printing process results in characteristic degradations in the printed image quality. Specifically, such velocity variations give rise to “banding” in the printed image. Certain frequencies of velocity variation in particular give rise to visually perceptible banding in the printed image, and the amplitude of those variations generally corresponds to the severity of banding.
Consequently, EP systems require accurate velocity control. In particular, EP systems require tight velocity control at least for certain process members to minimize velocity variations during times when those process members are meant to have nominally constant velocities. However, because the driven velocity of a process member depends on a complex (and sometimes) conflicting assortment of drive train and control variables, achieving tight velocity control is a difficult challenge at best.
For example, an experienced system designer might specify inherently high quality motors, motor controllers, and drive train gear assemblies, and might build in a certain amount of mechanical “tuning” to allow tweaking of the completed assemblies for better performance, but economic and practical considerations limit these kinds of solutions. In the end, even with quality parts, careful assembly, and in-system tuning, it is difficult to suppress fully the objectionable printed image banding that arises from process member velocity variations.
Of course, EP systems represent just one example of the need for tight velocity control. A host of other devices and systems, such as those systems used in precision positioning control, require tight velocity control.